A. Field of the Invention
The invention relates to a damper mechanism and particularly a damper mechanism for damping torsional vibrations in a power transmission system.
B. Description of the Background Art
Clutch disk assemblies used with a clutch cover assembly in vehicles are generally for the purpose of providing a means for engaging and disengaging the clutch disk assembly to and from a flywheel for transmitting torque. Such clutch disk assemblies also often include members which provide a dampening function for absorbing and damping vibrations transmitted from the flywheel. Generally, such vibrations are most noticeable as idling noises (rattle), driving noises (acceleration/deceleration rattle and muffled noises) and tip-in/tip-out (low frequency vibrations). Clutch disk assemblies having dampening capabilities are usually effective for removing these noises and vibrations.
The idling noises are rattling noises which occur from a transmission when the transmission gears are in a neutral position, e.g., during waiting at traffic signals with clutch pedal off. This rattling occurs due to the fact that an engine torque is in a low RPM engine idling range and engine combustion causes large torque variations.
The tip-in/tip-out (low frequency vibrations) are large longitudinal vibrations in the drive train of a vehicle which occur when a driver rapidly depresses or releases an accelerator. Such rapid changes in acceleration cause a correspondingly rapid response from the drive train in the vehicle, which may be characterized as a stepwise change in torque (as opposed to a gradual or smooth change in torque). When torque is transmitted stepwise to the drive train, transitional vibrations occur. As a result, torque transmitted to the wheels of the vehicle may be reflected or transmitted back from the wheels through the drive train and clutch (an oscillation of the torque). Consequently, the entire body of the vehicle may undergo some transitional vibration. Such vibrations are disturbing to the driver and passengers in the vehicle.
Dampening noises during idling is difficult where no torque is being transmitted through a clutch disk assembly because low torsional rigidity is preferable to dampen such noises. However, in order to dampen other forms of vibration in the clutch disk assembly, a high torsional rigidity is preferable in this region. In other words, for some situation, low rigidity is desirable and other situations, a high rigidity is desirable. A clutch disk assembly has been provided with soft springs (less rigidity) for achieving nonlinear torsion characteristics providing a low rigidity in a first portion of the overall displacement range of a clutch disk assembly, and has also been provided with rigid springs to provide a high level of rigidity in a second portion of the displacement range of the clutch disk assembly. In such a clutch disk assembly, the torsional rigidity and hysteresis torque in the first stage are low so that idling noises can be prevented effectively.
When low frequency vibrations are supplied to the damper mechanism in the conventional clutch disk assembly described above, the damper mechanism repeatedly may undergo torsion or twisting movements (relative rotary displacement between dampening members) over a wide angular range in opposite directions, where the displacement angle may be measured from a torsion free state between the positive and negative displacement ranges. In this operation, the low frequency vibrations may not be damped sufficiently because the characteristics in the displacement range have a nonlinear form.
An object of the invention is to allow effective damping of torsional vibrations caused by torsion in and between positive and negative second stages in a damper mechanism having at least two stages of torsion characteristics.
In accordance with one aspect of the present invention, a damper mechanism includes a first rotary member and a second rotary member disposed adjacent to the first rotary member for limited relative rotary displacement with respect to one another about a central rotary axis. The limited relative rotary displacement is defined by a torsion angle xcex84. Within the limited relative rotary displacement, a first stage of relative rotary displacement is defined by first torsion angle xcex81 that is smaller than the torsion angle xcex84. A first damper mechanism is provided for circumferentially and elastically coupling the first and second rotary members together, and includes a first elastic member arranged between the first and second rotary members for transmitting torque therebetween. However, the first elastic member is not compressed in response to relative rotary displacement within the first torsion angle xcex81. A second damper mechanism is disposed adjacent to the first and second rotary members for operation in parallel with the first damper mechanism for circumferentially and elastically coupling the first and second rotary members together. The second damper mechanism includes a first intermediate member operably disposed between the first and second rotary members for rotating relative to the first rotary member within a torsion angle xcex8AC that is smaller than the first torsion angle xcex81. The second damper mechanism also includes a second elastic member arranged between the first intermediate member and the first rotary member for circumferentially and elastically coupling the first intermediate member and the first rotary member together, the second elastic member having a lower rigidity than the first elastic member. The second damper mechanism further includes a friction mechanism provided between the first intermediate member and the second rotary member for creating friction in response to relative rotation between the first intermediate member and the second rotary member.
In one embodiment of the present invention, the first and second rotary members are formed with corresponding windows. The first elastic member is disposed in both of the windows. The window in the second rotary member has a circumferential length greater than a circumferential length in the window in the first rotary member. The first torsion angle xcex81 is defined by the difference in circumferential length in the windows in the first and second rotary members.
In another embodiment, the second rotary member includes a hub formed with a hub flange and a flange disposed about the hub flange. The hub flange is formed with gear teeth on a radial outer surface thereof. The flange is formed with gear teeth on a radially inner surface circumferentially spaced apart from the gear teeth on the hub flange thereby defining the first torsion angle xcex81.
Preferably, a portion of the first rotary member defines an annular space between the portion of the first rotary member and the hub flange. The friction mechanism, the second elastic member and the first intermediate member are at least partially disposed in the annular space.
Preferably, the second damper mechanism provides vibration dampening throughout all of the limited relative rotary displacement between the first and second rotary members defined within the torsion angle xcex84.
Preferably, the first rotary member is at least partially defined by a pair of plates, a first of the plates being formed with the portion for defining the annular space.
Preferably, the friction mechanism further includes a friction washer disposed between a second of the pair of plates and the hub flange for creating friction in response to relative rotation therebetween.
Preferably, the friction mechanism further includes a friction washer disposed between the first of the pair of plates and the first intermediate member for creating friction in response to relative rotation therebetween.
Preferably, the friction mechanism further includes a friction washer disposed between the hub and the first intermediate member for creating friction in response to relative rotation therebetween.
Preferably, the second elastic member is retained by the first of the pair of plates.
Preferably, the second elastic member is retained by a retaining member that is fixed to the first of the pair of plates.
Preferably, the retaining member is made of a resin material.
Static torsion characteristics of the damper mechanism are as follows. A first stage in the torsion characteristics is defined between zero torsion and the first torsion angle, and a second stage is defined between the first torsion angle and a second torsion angle, which is larger than the first torsion angle. In a range smaller than the second torsion angle within the first stage, the second elastic member is compressed between the first intermediate member of the second damper mechanism and the first rotary member. When the torsion angle exceeds the second torsion angle, the second elastic member is no longer compressed, and the friction mechanism generates a hysteresis torque between the first intermediate member and the second rotary member. This provides the first stage characteristics of zero rigidity and a high hysteresis torque. When the torsion angle exceeds the first torsion angle and enters the second stage, the first elastic member is compressed between the first and second rotary members so that second characteristics of a high rigidity and a high hysteresis torque are achieved.
When torsion occurs in and between the positive and negative second stages of the torsion characteristics, a high hysteresis torque occurs in the positive and negative first stages between the positive and negative second stages. As described above, the friction mechanism operates in the region of the first stage to produce the high hysteresis torque. Therefore, low frequency vibrations such as tip-in/tip-out can be effectively damped.
When the damper mechanism is supplied with minute vibrations of a small amplitude in the first and second stages, no slide occurs in the friction mechanism so that the characteristics of a low hysteresis torque are achieved. In this state, the damper mechanism operates through an angular range substantially twice as large as the second torsion angle.